The Science Underpinning Anomalous Scaling Laws of Strength and Toughness in Nanocellulose Materials

在先进的材料设计中，对高强度和高韧性材料的追求是永恒的。不幸的是，这两种机械性能通常是相互排斥的。例如，对于金属和合金，它们的韧性通常与强度成反比。因此，在实践中，设计坚固和坚韧的材料是不可避免的妥协。到目前为止，解决强度与韧性冲突的普遍可行的机制仍然难以捉摸。该项目计划通过研究纤维素纳米纸机械性能异常但理想的标度规律的基础科学，揭示解决强度与韧性冲突的可能策略：随着纤维素纤维尺寸的减小，其强度和韧性都会增加。这些独特的特性与纤维素纸固有的生物降解性、低成本和可扩展的制造相结合，可以对具有理想机械性能的高性能材料的自下而上设计产生重大影响。研究计划将在多尺度力学建模与互补实验相结合的系统框架下进行，由两个推力组成。推力1的总体目标是通过多尺度力学建模和互补实验，研究纤维素分子链、纳米纤化纤维素纤维和纤维素纤维网络的力学，从而定量了解强韧性纤维素纳米纸的基础机制。推力1的基本理解将为推力2的研究工作奠定坚实的基础，推力2的重点是概括获得强度和韧性的基础机制，以指导探索一类具有其他高度期望的多功能的强韧材料。跨学科的研究生培训将使学生能够访问NIST世界一流的成像和计量设施，并从世界领先的造纸公司学习大量的专业知识和最先进的技术。推广活动将通过iMechanica.org进行，iMechanica.org是最大的国际机械在线社区，拥有50,000多名注册用户。

The quest of materials possessing both high strength and high toughness is perpetual in advanced material design. Unfortunately, these two mechanical properties are generally mutually exclusive. For example, for metals and alloys, their toughness is usually inversely proportional to their strength. As a result, in practice, the design of strong and tough materials is inevitably a compromise. So far, a general and feasible mechanism to address the conflict of strength vs. toughness still remains elusive. This project plans to shed insight on a possible strategy resolving the conflict of strength vs. toughness by investigating the fundamental science of the anomalous but desirable scaling law of mechanical properties of cellulose nanopaper: both its strength and toughness increase as the cellulose fiber size decreases. These unique features combined with the intrinsic biodegradability, low-cost and scalable manufacturing of cellulose paper can have significant impact on bottom-up design of high performance materials with desirable mechanical properties. The research plan will be carried out in a systematic framework integrating multi-scale mechanics modeling and complementary experiments and consists of two thrusts. The overarching goal of Thrust 1 is to establish a quantitative understanding of the underpinning mechanism of both strong and tough cellulose nanopaper, by investigating the mechanics of cellulose molecular chains, nanofibrillated cellulose fibers and cellulose fiber network via multi-scale mechanics modeling and complementary experiments. The fundamental understanding from Thrust 1 will lay out a solid foundation that motivates and enables the research efforts in Thrust 2, which focuses on generalizing the underpinning mechanism of attaining both strength and toughness to guide the exploration of a class of strong and tough materials with other highly desirable multi-functionalities. Interdisciplinary graduate student training will enable to access world-class imaging and metrology facilities at NIST, and to learn from the vast expertise and state-of the-art technology from a world leading paper company. Outreach activities will be conducted via iMechanica.org, the largest international online community of mechanics with 50,000+ registered users.